N-phosphonomethylglycine, commonly referred to as glyphosate, is an important agronomic chemical. Glyphosate inhibits the enzyme that converts phosphoenolpyruvic acid (PEP) and 3-phosphoshikimic acid to 5-enolpyruvyl-3-phosphoshikimic acid. Inhibition of this enzyme (5-enolpyruvylshikimate-3-phosphate synthase; referred to herein as “EPSPS”) kills plant cells by shutting down the shikimate pathway, thereby inhibiting aromatic amino acid biosynthesis. Inhibition of aromatic amino acid biosynthesis kills plant cells as well as some bacterial cells. Glyphosate is an effective, broad-spectrum systemic herbicide used to kill weeds and is the most widely used herbicide in the United States.
EPSPS enzymes are broadly categorized into three groups: Class I, Class II and Class Ill. Mutations in Class I EPSPS genes are known that provide tolerance to glyphosate's inhibitory activity. For example, Glyphosate tolerance in plants can be achieved by the expression of a modified Class I EPSPS that has lower affinity for glyphosate, yet still retains its catalytic activity in the presence of glyphosate (U.S. Pat. Nos. 4,535,060, 6,040,497, and 7,723,575). “Tolerate”, “tolerance”, “resist” or “resistance” is intended to mean that a plant can either survive, or carry out essential cellular functions such as protein synthesis and respiration in the presence of an herbicide, particularly glyphosate, in a manner that is not readily discernible from untreated cells. Class I EPSPS genes can be found in a variety of backgrounds, including plants, algae and microorganism such as bacteria. Well-known Class I genes are derived from Zea mays (corn) and E. coli (where the gene is known as aroA).
Class II and Class III EPSPSs have been isolated from bacteria that are naturally resistant to glyphosate and when the enzyme is expressed as a transgene in plants provides glyphosate tolerance to the plants (Ex. U.S. Pat. Nos. 5,633,435, 5,094,945 and 7,534,937).
Crop plants that comprise one of the tolerant EPSPSs from Class I, II or III are tolerant to glyphosate and allow glyphosate to be used for effective weed control with minimal concern of crop damage. For example, glyphosate tolerance has been genetically engineered into corn (U.S. Pat. No. 5,554,798), wheat (Zhou et al. Plant Cell Rep. 15:159-163, 1995), soybean (WO 9200377), sugarbeet (U.S. Pat. No. 7,335,816), and canola (WO 9204449).
There is a great need in plant molecular biology for a diversity of genes that can provide a selectable marker phenotype. Tolerant EPSPS enzymes are useful as selectable markers during transformation where glyphosate selection is used, i.e. where transformed plant cells comprising the tolerant EPSPS are selected due to their ability to survive on glyphosate-containing media. The present invention provides DNA and protein compositions of a glyphosate tolerant variant Class I EPSPS enzyme. The present invention also provides DNA constructs useful in plants and transgenic plants that exhibit glyphosate tolerance.